This invention relates to an improved elevator assembly adapted for use with a well-drilling apparatus preferably, a top head drive type of such apparatus, in order to lift or lower drilling or production tubulars quickly and efficiently. This invention is equally applicable to running drill strings, consisting of diverse sizes of drill collars and drill pipe, into or out of a well bore, and to running diverse sizes of casing or production tubing into or out of a well bore, and all with or without rotating the string of tubulars in the hole and with or without circulating mud or other fluids through the string of tubulars.
In a wide variety of well-drilling operations, it is necessary to assemble a drill string from a large nuxber of individual lengths of drill pipe as a borehole is being drilled. When it becomes necessary for any reason to remove the drill string from a borehole, as, for example, to replace worn drill bits, the drill string must be progressively raised as successive lengths of drill pipe are brought to the surface and removed from the drill string. Well servicing requires similar equipment, which, in smaller sizing, is used to pull or replace sucker rods, production piping, etc., for pump service, replacement of worn pipes or rods, or during well cleanout to improve production.
One type of drilling apparatus in widespread use utilizes a power swivel which is threadedly coupled to the uppermost length of drill pipe and then used to raise the drill string and to remove the uppermost length of drill pipe from the string. Once this has been accomplished, the threaded connection between the power swivel and the uppermost length of drill pipe is broken; and means, such as a transfer arm, can then be used to move the length of drill pipe from the vertical position aligned with the borehole to a horizontal position at ground level.
This prior art approach to raising a drill string and successively removing lengths of drill pipe from the string is not entirely acceptable It requires that the power swivel be threadedly coupled to each successive length of drill pipe and that this threaded connection then be broken. These repeated threading and unthreading operations can significantly slow the rate at which drill pipe can be removed from a borehole, and, in addition, can cause undesirable wear on the threaded connections of the swivel and of the drill pipe.
It is, therefore, an object of this invention to provide an improved apparatus useful in removing drill pipe from a borehole and, in particular, to provide such an apparatus which does not require threaded connections between the apparatus and the drill pipe and which can be used to increase the rate at which drill pipe can be removed from a borehole.
A further object of the invention is to provide an elevator for drill pipe that will operate reliably at any angle, and not only in a substantially vertical mode.
An additional object of the invention is to provide an elevator that can be controlled from a remote location and that will provide increased safety and reliability in operation.